The present invention relates, in general, to electronics, and more particularly, to semiconductors, structures thereof, and methods of forming semiconductor devices.
In the past, the semiconductor industry utilized various methods and structures to form transient suppression devices (TSD). These transient suppression devices typically were utilized to protect electronic equipment from transient electrical disturbances such as an electrostatic discharge (ESD) or electromagnetically coupled interference. The transient electrical disturbances generally occurred at the terminals of electronic devices such as at the input and output terminals. The transient electrical disturbances could damage the electronics of the devices therefore the transient suppression devices were attached to the terminals of the electronic device to minimize damage. The transient suppression devices typically were zener diodes or a transistor coupled in a diode configuration. The transient suppressor devices typically had a high impedance which resulted in a large voltage change across the transient suppression device as the current conducted by the transient suppression device increased. The impedance usually was in the order of one to ten (1-10) ohms. Consequently, the knee of the V-I characteristic curve was soft.
Technology advancements lead to electronic devices operating at lower voltages. Because the voltage across the transient suppressor device increased as the conducted current increased, the prior transient suppression device generally was not able to adequately protect electronic devices that operated at lower voltages such as voltages below about five volts (5 V) and especially voltages at lower voltages such as three volts (3 V) or one and eight tenths of a volt (1.8 V) or less.
Accordingly, it is desirable to have a transient suppression device that has a lower impedance, that has a sharper knee of the V-I characteristic curve, that has a lower leakage current, and that operates at voltages of less than about five volts (5 V).
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are reasonable variances from the ideal goal of exactly as described. For clarity of the drawings, doped regions of device structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions generally may not be straight lines and the corners may not be precise angles.